Three phase

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RichardM

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Just a quickie: Someone is arguing with me whether 480/277 is always wye or not.
Could you please reassure me that I am not insane?
 
George Stolz said:
Delta voltages are always halved - 240/120.

Wye voltages are always different - 208/120Y, 480/277Y
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I always thought 240/120 single phase voltages were different than 208/120 3phase due to phase angel, you can get 240/120 phase but aren't the windings in the transformer different for that voltage?
 
The winding ratio is the same for 240/120 3? and 208/120 3?.

120/240 single phase is entirely different - it's just a single phase of 240. It's derived from a single phase of a higher voltage, not all three phases.

It's a single phase of 240V with a tap in the middle of it, to give us a point where we can get 120V instead of the full 240V.
 
LarryFine said:
Is the derived neutral not effectively of a wye configuration?
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I don't know. My thoughts were:

1) The transformer secondary is _not_ a wye.

2) As far as fundamental component current flow, the composite transformer secondary looks like a wye.

3) IMHO the key distinction will be how the composite secondary responds to harmonic current flow, and if this response is different from that of a true wye secondary. But at this point the analysis is beyond what I can do on a quick hunch; I'd need to sit down and plot various impedances.

-Jon
 
George Stolz said:
The winding ratio is the same for 240/120 3? and 208/120 3?.

120/240 single phase is entirely different - it's just a single phase of 240. It's derived from a single phase of a higher voltage, not all three phases.

It's a single phase of 240V with a tap in the middle of it, to give us a point where we can get 120V instead of the full 240V.
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Ok, then how do you get 240/120 3 phase. I use several 480 to 208/120 3 phase transformers, never installed a 240 3phase version.
 
gbudke said:
Ok, then how do you get 240/120 3 phase. I use several 480 to 208/120 3 phase transformers, never installed a 240 3phase version.
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240/120 3ph is three 240v secondaries in a Delta configuration, with the center tap of one secondary grounded, which is why the opposing phase has a higher-to-ground voltage.

From the neutral point of view, the 120/240v section is identical to your home service. In fact, the open Delta began as a three-phase conversion of an existing single-phase service.

208/120 3ph is three 120v secondaries in a wye configuration. Often three 120/240v transformers have the internal links reconnected, using only two of the three secondary bushings.
 
Technically the IEEE/ANSI correct voltage designations are:
480Y/277 = 480V L-L, 277V L-N 3 Phase, 4 Wires, wye configuration
208Y/120 = 208V L-L, 120V L-N 3 Phase, 4 Wires, wye configuration
240/120 = 240V L-L, 120V L-N (high leg 208V not used), 3 Phase, 4 Wires, delta configuration

I am not aware of any recognized method for expressing the voltages of an "open-wye" MWBC (2 lines + neutral). I have tried to call these
120/208 1 phase 3 wire and 277/480 1 phase 3 wire. One of the local POCOs uses the phrase "single phase 120/208 network".
 
jim dungar said:
Technically the IEEE/ANSI correct voltage designations are:
480Y/277 = 480V L-L, 277V L-N 3 Phase, 4 Wires, wye configuration
208Y/120 = 208V L-L, 120V L-N 3 Phase, 4 Wires, wye configuration
240/120 = 240V L-L, 120V L-N (high leg 208V not used), 3 Phase, 4 Wires, delta configuration . . .
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Do you know then how they designate single-phase 240/120?
 
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